The present invention refers, in a first aspect, to a method for cutting a workpiece by means of a beam-shaped fluid cutting medium ejected under high pressure out of a nozzle, whereby there is provided a high-pressure fluid jet escaping from the nozzle, whereby the high-pressure fluid jet is directed against the workpiece, and whereby the nozzle is moved over the surface of the workpiece along a predetermined path.
According to a second aspect, the invention refers to an apparatus for cutting a plain, curved or arched workpiece by means of a beam-shaped fluid cutting medium ejected under high pressure out of a nozzle. This apparatus comprises a nozzle provided at the end of a tube-like member and means for providing a high-pressure fluid jet escaping from the nozzle.
It is well known in the prior art to cut or separate workpieces in a touchless method by means of a fluid jet, a gas jet or a laser beam, said jet or beam being directed towards the workpiece to be cut and being moved along a desired path. Probably the most common apparatusses of this kind are the water jet cutting apparatusses which use a water jet ejected from a nozzle under a pressure of up to 4000 bar. Thereby, it is possible to cut workpieces of different kind, e.g. styropor, wood, fabrics, leather, rubber, textiles and many more.
It is also known in the prior art art to admix an abrasive medium to this fluid jet, e.g. quartz, glass dust, corundum etc. in order to be able to cut harder materials like metal, glass, stone and the like.
According to the prior art, it has been taught to direct the fluid jet exactly perpendicularly towards the surface of the workpiece to be cut in order to get an exact and clean cut edge. This perpendicular position had to be maintained during the entire cutting process, even if the movement of the cutting jet is controlled by a CAD-machine.
However, experience has shown that this is not true; in this manner, it is not possible to achieve a cleanly cut edge. Particularly, the edges of the cut workpieces are not exactly cut, are irregular and do not extend exactly perpendicularly to the plain surface of the workpiece.
As can be seen from FIG. 1, for example, in cutting a plate-like workpiece 1 by means of a fluid jet-like cutting medium 2 being ejected from a nozzle 3, it is not possible to achieve an exactly cut edge surface 4 because, as a result, the angle 5 is smaller or larger than 90.degree. with reference to the surface 6 of the workpiece 1. This situation is schematically shown in FIG. 1. However, if it is required to very exactly cut a workpiece, the aforementioned disadvantages occur particularly aggravatingly. If, for example, precisely shaped parts have to be cut out of a workpiece according to a complicated shape which, thereafter, have to be inserted into correspondingly negative shaped workpieces or which have to be assembled with other precise workpieces, it is of paramount importance that the cut edges exactly run parallelly with regard to the workpieces.
For example, if cut-out parts, e.g. letters, are to be inserted into corresponding cut-outs of a base plate in order to manufacture inlays or high relief printings, the cut edges of the letters are allowed to be inclined inwards, but not outwards. With other words, deviations from the perpendicular direction can be tolerated in one, but only in one direction and not in the other direction. However, according to the prior art, deviations from the perpendicular direction of the cut edge surface can not be avoided because no reliable and economic method exists to provide an exactly perpendicular and clean cut edge.
The only method to avoid the aforementioned disadvantages known in the prior art was to drastically reduce the cutting speed during the cutting or separating process. A cut edge surface which is practically usable can be achieved, according to the prior art, if the theoretically possible cutting speed, depending on the material to be cut and on the cutting medium used, is not really exploited, but considerably reduced. However, such a proceeding results in a considerably loss of efficiency with the consequence that the final product becomes much more expensive. The reason is that the very expensive cutting apparatusses can not be used according to their theoretical possibilities.